Gametogenesis in animals is to be studied from three major standpoints: (1) The interactions of X-heterochromatin in gametic behavior; (2) The relationship of translocations to male sterility; (3) Genetic and biochemical regulatory factors in the process of spermiogenesis. Heterochromatin of the X-chromosome will be examined in relation to the occurrence of parthenogenesis in mice, particularly with respect to the possibility that failure of x-inactivation may be a major factor in limiting the success of parthenogenotes. A detailed analysis of the role of X-heterochromatin in the normal development of Drosophila sperm will be undertaken, the principal objective being the identification of the site in the heterochromatin that is responsible for sperm head elongation. Various combinations of autosome-sex chromosome translocations will be used to determine whether a parallel may be found between mice and Drosophila with respect to the effects of autosomal translocations on fertility in the male. The problems of spermiogenesis will also be approached from a development standpoint. Early events in testicular determination will be sought out by analyses of mosaics. The relationship between premeitotic DNA synthesis and the last premeiotic cell cycle will be probed. Proteins peculiar to meiosis will be further characterized both with respect to recombinational mechanisms and also with respect to chromosome compaction, particularly during latter stages of spermiogenesis. Fine structural studies of spermiogenesis in Drosophila as they relate to genetic lesions causing male infertility will be continued. BIBLIOGRAPHIC REFERENCES: Hotta, Yasuo and Herbert Stern. Persistent discontinuities in late replicating DNA during meiosis in Lilium,. Chromosoma (in press) (1976). Stern, Herbert and Yasuo Hotta. Biochemistry of Meiosis. Proc. R. Soc. Lond. (in press) (1976).